1. Field of the Invention
The present invention relates to an apparatus for producing a vertical center line in a television type game machine.
2. Description of the Prior Art
Traditionally, apparatus for producing a vertical center line in a television game machine has utilized the horizontal fly-back line signal of the rastor display as a trigger signal to the gate of a monostable multi-vibrator. In the prior art, the rise or fall of this trigger signal is timed so as to be located between the consecutive horizontal fly-back line signals in order to obtain proper placement of the vertical center line on the display device screen. Additional circuit stages must be used in conjunction with the monostable multi-vibrator stage in order that the center line waveform is differentiated and suitably shaped. The prior art devices for producing center lines in television-type game machines have been plagued with stability problems inherent in monostable multi-vibrator circuits. As a result, high tolerances of component values are required with consequently higher costs. Moreover, because of the additional circuitry necessary to implement the prior art apparatus, additional component, manufacturing and testing costs are incurred. The present invention overcomes the inherent high cost and complexity of the prior art by providing a simplified circuit arrangement that is more accurate, is highly stable and is less costly to construct and maintain.